They share a name – David – and a passion for nature. For a while they also shared a place in the vanguard of nature documentary-making, broadcasting from every corner of the globe to the homes of millions. But while one, Attenborough, basks in the glow of national treasure status, the other claims he is now a pariah.

"You're early," David Bellamy roars, dropping the wheelbarrow he is pushing around his four-acre garden in Co Durham. He strides towards me, all rolling gait, unruly white hair and beard. "Go inside while I just finish off."

Though he turns 80 next Friday, Bellamy has a remarkable physique for a man his age, over 6ft tall and slender, muscular even, despite a little trouble when he walks. The voice and appearance have stayed in pretty good nick since his heyday as a scientist, conservationist and TV personality. He was a household name, inspiring Lenny Henry's "grapple me grapenuts" catchphrase and even a Ribena commercial.But for the grace of God he would be revered as the man who brought botany to life through glorious rambling monologues in a time before CGI graphics and hi-tech film techniques became de rigueur. But his fame and acclaim rolled off the rails in 2004 when – in the teeth of public opinion and mounting scientific evidence – he said global warming was nothing but "poppycock". He was deserted by fans, shunned by peers and, he says, ostracised by broadcasters and conservation groups that once thrived through his endorsement: he was sacked as president of the Wildlife Trusts.

Bellamy, who appears not to be able to shake the habit of speaking as if the camera were still rolling, is unrepentant. He is clear his stance on climate change ended his TV career. Some point out that an ill-fated dip into politics before this, standing against the then Prime Minister John Major in Huntingdon in the 1997 general election for the Referendum Party, cannot have helped.

Nevertheless, in a flurry of rapid hand gestures, gravelly voice – oscillating between whisper and oratory – through the filter of that full beard, he is unequivocal. "All of the work dried up after that. I was due to start another series with the BBC but that didn't go anywhere, and the other side [ITV] didn't want to know. I was shunned. They didn't want to hear the other side." But does he still believe he is right? "Absolutely. It is not happening at all, but if you get the idea that people's children will die because of CO2 they fall for it," he says, perhaps buoyed by forecasters at the Met Office this week downgrading a prediction for global warming to suggest that by 2017 average temperatures will have remained about the same for two decades.